In an automobile engine, rotation of a crankshaft is transmitted to a camshaft by means of a timing chain (hereinafter, simply referred to as a “chain”), to open and close valves of combustion chambers by rotating the camshaft.
Chain transmission devices are used to drive such camshafts. Many of such chain transmission devices include a driving sprocket attached to the crankshaft, a driven sprocket attached to the camshaft, a chain trained around the driving sprocket and the driven sprocket, a pivotable chain guide arranged at the loose side of the chain, a chain tensioner pressing the chain guide against the chain, and a fixed chain guide arranged at the tension side of the chain.
The pivotable chain guide is biased by the chain tensioner, so as to press the chain. As a result thereof, tension of the chain is kept constant. The fixed chain guide controls vibration of the chain while keeping an ideal travelling line of the chain.
As the pivotable chain guide or the fixed chain guide, which is used in the above chain transmission devices, sliding type chain guides are known of which the guiding surface extending along the travel direction of the chain is brought into sliding contact with the chain. Since the chain guides of this type are brought into sliding contact with the chain, resistance to travelling of the chain is large. Therefore, transmission loss of torque is large.
In order to overcome this problem, the inventors of the present invention have proposed in the below-identified Patent document 1 a chain guide including a plurality of rollers spaced apart from each other along the travel direction of the chain such that the chain is guided by the respective rollers.
Since this chain guide is in rolling contact with the chain (rolling type), resistance to travelling of the chain is small. Therefore, transmission loss of torque is small.